Satellite earth terminals receive downlink streams from one or more satellite transponders, for example, operating in the C/Ku frequency bands. High bandwidth signals, such as multimedia signals, are generally received from a satellite using a high gain antenna. An example of such an antenna includes a dish reflector directing energy into a feed horn. The received broadcast signals, or streams, are generally grouped according to satellite transponders, with each transponder assigned a respective non-overlapping portion of the spectrum, or bandwidth. The received satellite signals are amplified and down converted, for example, by a device commonly referred to as an LNB—a combined Low Noise Amplifier (LNA) and block down converter. The LNB is typically located as close as possible to the satellite feed horn, down converting a group of transponder signals (e.g., sixteen) to an intermediate frequency. It is common in video broadcast applications for the intermediate frequency to be located within a portion of the electromagnetic spectrum referred to as L-band.
L-band represents a crowded region of the electromagnetic spectrum, supporting many activities, such as aeronautical radio-navigation, radio astronomy and maritime mobile satellite. Use of this region of spectrum, as described herein, related to video broadcast satellite applications, is not considered by frequency management organizations, such as the Federal Communications Commission (FCC) in the allocation of authorized users. Use of the L-band by video broadcast satellite users, is considered unnecessary, as they are referred to as “wired carriers.” Although over-the-air signals are received in the C and Ku bands, the L-band intermediate frequency signals are transported from the LNB using cables or waveguides. Since the intermediate-frequency signals are protected from exposure to the ambient electromagnetic environment, it is presumed that sufficient protection from any radiated signals in the same frequency band will be provided by the wired carrier's cable or waveguide shielding. Unfortunately, problems can occur due to breaches in the cable or waveguide. Such breaches may result from corrosion, loose interconnections or water ingress. Such conditions left untreated would allow for ingress of ambient electromagnetic energy, which could, depending upon such features as amplitude, frequency and modulation, interfere with operation of the video broadcast satellite receiver system.
Fortunately, most of authorized L-band uses are relatively low power, such that any unwanted interference that happens to fall within the L-band may not result in perceptible interference to the video broadcast system. It may go undetected altogether. However, as utilization of the electromagnetic spectrum grows, it is likely that new applications may operate at higher levels. In particular, one potential application is 4G wireless broadband communications network that may operate terrestrial communications within the L-band (e.g., at 1525 and 1559 MHz). Such operations would likely operate at relatively high power, such that interference would result in perceptible interference.